CN115459619A - Fault-tolerant control method for redundant hot standby MMC - Google Patents
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- H02M7/44—Conversion of DC power input into AC power output without possibility of reversal by static converters
- H02M7/48—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5387—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
- H02M7/53871—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
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Abstract
本发明涉及一种冗余热备用MMC的容错控制方法，涉及MMC的子模块故障容错控制技术领域。本发明根据冗余热备用MMC数学模型计算出不对称相非对称环流电压表达式；再忽略谐波的影响，计算出奇数次环流表达式；然后忽略三次环流电压的影响，计算出基频环流表达式，得到注入基频电压的幅值和相位角；最后将基频电压注入不对称相参考电压中，采用最近电平逼近调制方法(NLM)进行子模块的投切。本发明简单易操作，适用于多个子模块多个桥臂不对称运行工况，有效抑制了MMC中的环流基频分量和谐波，明显减小了MMC的内部损耗，改善了MMC的输出电能质量。
The invention relates to a fault-tolerant control method of a redundant hot standby MMC, and relates to the technical field of fault-tolerant control of submodules of the MMC. The present invention calculates the asymmetric phase asymmetric circulation voltage expression according to the redundant hot standby MMC mathematical model; then ignores the influence of harmonics, calculates the odd number of circulation expressions; then ignores the influence of the third circulation voltage, and calculates the fundamental frequency circulation Expression to obtain the amplitude and phase angle of the injected fundamental frequency voltage; finally inject the fundamental frequency voltage into the asymmetrical phase reference voltage, and use the nearest level approximation modulation method (NLM) to switch the sub-modules. The invention is simple and easy to operate, is suitable for the asymmetrical operating conditions of multiple sub-modules and multiple bridge arms, effectively suppresses the fundamental frequency component and harmonics of the circulating current in the MMC, significantly reduces the internal loss of the MMC, and improves the output power of the MMC quality.
Description
技术领域technical field
本发明涉及一种冗余热备用MMC的容错控制方法，涉及MMC安全、可靠性运行技术领域，特别是涉及MMC的子模块故障容错控制技术领域。The invention relates to a fault-tolerant control method of a redundant hot standby MMC, and relates to the technical field of safe and reliable operation of the MMC, in particular to the technical field of the sub-module fault-tolerant control of the MMC.
背景技术Background technique
模块化多电平换流器(Modular Multilevel Converter，MMC)以模块化程度高、输出波形质量好、器件开关频率低等特点，被广泛应用于高压直流输电(High VoltageDirect Current,HVDC)与海上风电并网等领域。MMC的优点来源于其子模块级联的结构，然而MMC中所包含的大量级联子模块同时也构成了潜在故障点，这对MMC的运行可靠性带来了极大的挑战。Modular Multilevel Converter (MMC) is widely used in high voltage direct current transmission (High Voltage Direct Current, HVDC) and offshore wind power due to its high modularity, good output waveform quality, and low device switching frequency. grid and other fields. The advantage of MMC comes from its sub-module cascading structure. However, a large number of cascading sub-modules contained in MMC also constitute potential failure points, which poses a great challenge to the operation reliability of MMC.
为了提高MMC运行的可靠性，采用冗余子模块热备用工作模式以提高MMC子模块故障容错性能。冗余子模块热备用工作模式将包含冗余子模块在内的所有子模块投入运行，在子模块故障时通过直接旁路故障子模块，不减少投入子模块数目，保证MMC不间断工作，该工作模式具有简单可靠、可无缝切换的优点。但由于实际运行中各相之间以及每相上、下桥臂子模块故障数目不一致，将导致各系统因不对称运行而产生环流增大，输出电流畸变、电容电压纹波较大、直流电流波动过大等问题。In order to improve the reliability of MMC operation, the redundant sub-module hot standby mode is adopted to improve the fault-tolerant performance of MMC sub-module. Redundant sub-module hot standby mode puts all sub-modules including redundant sub-modules into operation. When a sub-module fails, it directly bypasses the faulty sub-module without reducing the number of input sub-modules, ensuring uninterrupted operation of the MMC. The working mode has the advantages of being simple, reliable and seamlessly switchable. However, due to the inconsistency in the number of faults between the phases and the sub-modules of the upper and lower bridge arms of each phase in actual operation, it will lead to increased circulation of the systems due to asymmetrical operation, output current distortion, large capacitor voltage ripple, and DC current problems such as excessive fluctuations.
故障子模块切除后因不对称运行而增大的环流可以通过冗错控制得以抑制,包括控制桥臂能量平衡，改变中性点在故障相电压矢量方向的移位，引入虚拟电阻等解决方案。但是其中研究对象的调制策略绝大多数都是基于脉冲宽度调制(Pulse WidthModulation，PWM)，对基于最近电平调制(Nearest Level Modulation,NLM)的相关研究还很少。具有NLM的MMC具有开关频率低、易于实现的特点，广泛应用于子模块数量较多的高压场合，现有的基于PWM的开路故障定位和容错控制方法并不直接适用。The increased circulating current due to asymmetric operation after the faulty sub-module is removed can be suppressed through redundant fault control, including controlling the energy balance of the bridge arm, changing the shift of the neutral point in the direction of the faulty phase voltage vector, and introducing virtual resistance and other solutions. However, most of the modulation strategies of the research objects are based on Pulse Width Modulation (PWM), and there are few related studies based on Nearest Level Modulation (NLM). MMC with NLM has the characteristics of low switching frequency and easy implementation, and is widely used in high-voltage applications with a large number of sub-modules. The existing PWM-based open-circuit fault location and fault-tolerant control methods are not directly applicable.
目前对于热备用MMC的容错控制方法包括：在正常运行期间降低子模块电容器电压，这样开关和电容器都具有较低的电压应力和较长的使用寿命；让所有桥臂切除子模块使得所有桥臂投入子模块数相同，这种方法将在容错操作期间保持对称的输出特性，但将导致可靠性降低；通过修改子模块电容器电压参考、调制波以及载波的频移和相移角度，MMC的输出特性仍然可以是对称的，没有电压不匹配。然而，这种容错过程仍然很复杂，尤其是载波重配置操作。本文提出的不对称容错控制策略同时具有以上这些容错控制方法的优点，而且方法简单易操作，适用于多个子模块多个桥臂不对称运行工况。The current fault-tolerant control methods for hot standby MMC include: reducing the sub-module capacitor voltage during normal operation, so that switches and capacitors have lower voltage stress and longer service life; Input the same number of sub-modules, this method will maintain symmetrical output characteristics during fault-tolerant operation, but will lead to reduced reliability; by modifying the sub-module capacitor voltage reference, modulation wave and carrier frequency shift and phase shift angle, the output of MMC The characteristics can still be symmetrical with no voltage mismatch. However, this fault tolerance process is still complicated, especially the carrier reconfiguration operation. The asymmetric fault-tolerant control strategy proposed in this paper has the advantages of the above-mentioned fault-tolerant control methods at the same time, and the method is simple and easy to operate, and is suitable for the asymmetrical operating conditions of multiple sub-modules and multiple bridge arms.
发明内容Contents of the invention
本发明要解决的技术问题是针对基于最近电平调制方法(nearest levelmodulation,NLM)的冗余热备用模块化多电平换流器(modular multilevel converter,MMC)，提供一种冗余热备用MMC的容错控制方法，用以解决上述问题。The technical problem to be solved by the present invention is to provide a redundant hot standby MMC for a redundant hot standby modular multilevel converter (MMC) based on the nearest level modulation method (nearest level modulation, NLM) The fault-tolerant control method is used to solve the above problems.
本发明的技术方案是：一种冗余热备用MMC的容错控制方法，当冗余热备用MMC因切除故障子模块上下桥臂子模块数目不相等时，采用注入基频电压的容错控制策略以抑制由于MMC结构不对称而产生的基频分量。The technical solution of the present invention is: a fault-tolerant control method of redundant hot standby MMC, when the number of upper and lower bridge arm sub-modules of the redundant hot standby MMC is not equal due to the removal of the faulty sub-module, the fault-tolerant control strategy of injecting the base frequency voltage is adopted to Suppresses the fundamental frequency component due to the asymmetry of the MMC structure.
具体步骤为：The specific steps are:
Step1：根据冗余热备用MMC数学模型计算出不对称相非对称环流电压表达式；Step1: Calculate the asymmetric phase asymmetric circulating current voltage expression according to the redundant hot standby MMC mathematical model;
Step2：忽略谐波的影响，计算出奇数次环流表达式；Step2: Neglecting the influence of harmonics, calculate the odd-numbered circulation expression;
Step3：忽略三次环流电压的影响，计算出基频环流表达式，得到注入基频电压的幅值和相位角；Step3: Neglecting the influence of the three-time circulating voltage, calculate the fundamental frequency circulating current expression, and obtain the amplitude and phase angle of the injected fundamental frequency voltage;
Step4：将Step3中的基频电压注入不对称相参考电压中，采用最近电平逼近调制方法(NLM)进行子模块的投切。Step4: Inject the fundamental frequency voltage in Step3 into the asymmetric phase reference voltage, and use the nearest level approach modulation method (NLM) to switch the sub-modules.
所述Step1具体为：The Step1 is specifically:
冗余热备用MMC每个桥臂中有n个子模块是维持桥臂输出电平数的必需子模块，剩余k个子模块为热备用子模块，n个子模块全部投入时桥臂端口电压与直流侧电压一致。因此，从直流侧电压的角度分析，任意时刻每个桥臂至少有k个子模块处于闲置状态。冗余度r是指MMC热备用冗余保护下冗余模块数与维持系统正常运行必需子模块数的比例关系，其具体为：There are n submodules in each bridge arm of the redundant hot standby MMC, which are necessary to maintain the output level of the bridge arm, and the remaining k submodules are hot standby submodules. The voltage is the same. Therefore, from the perspective of the DC side voltage, at least k sub-modules of each bridge arm are in an idle state at any time. Redundancy r refers to the proportional relationship between the number of redundant modules under MMC hot standby redundancy protection and the number of submodules necessary to maintain the normal operation of the system, which is specifically:
当有切除nf个故障子模块后，故障桥臂的冗余度rf为：When there are n f faulty sub-modules removed, the redundancy r f of the faulty bridge arm is:
其中，nf为故障子模块数。Among them, n f is the number of faulty sub-modules.
为了保证整个桥臂电压的输出电平数不变，子模块故障冗余率rf需不小于0，rf为0时意味着该桥臂没有冗余子模块，不对称相环流电压表达式为：In order to ensure that the output levels of the entire bridge arm voltage remain unchanged, the sub-module fault redundancy rate r f must not be less than 0. When r f is 0, it means that the bridge arm has no redundant sub-modules. The asymmetrical phase circulating voltage expression for:
式中，ucir_asym表示非对称环流分量，rfp，rfn分别表示上下桥臂的冗余比、Id表示环流中的直流分量、ih表示第h次环流谐波分量。In the formula, u cir_asym represents the asymmetric circulating current component, r fp and r fn respectively represent the redundancy ratio of the upper and lower bridge arms, I d represents the DC component in the circulating current, and i h represents the hth harmonic component of the circulating current.
所述Step2具体为：Described Step2 specifically is:
忽略谐波的影响，奇数次频分量的相环流电压表达式为：Neglecting the influence of harmonics, the phase circulating voltage expression of odd frequency components is:
式中，ucir_odd表示奇数次分量，包含基频和三倍频分量。In the formula, u cir_odd represents an odd-numbered component, including fundamental frequency and triple frequency components.
所述Step3具体为：The Step3 is specifically:
忽略三次环流的影响，得到基频环流的表达式：Neglecting the influence of the three-time circulation, the expression of the fundamental frequency circulation is obtained:
式中，ucir_1表示基频分量。In the formula, u cir_1 represents the fundamental frequency component.
大量级联子模块是MMC潜在的故障点，对MMC的运行可靠性带来了极大的挑战。一旦切除故障子模块，MMC各桥臂子模块数目不相等而工作于不对称模式。本发明公开一种冗余热备用MMC的容错控制方法，在不对称相引入了奇数次环流电压，其中基频分量较大，需要对MMC实现容错控制。该不对称环流导致MMC输出电流畸变、电容电压纹波较大、以及直流电流谐波和MMC损耗增大等问题。常规的环流控制器只能对二次环流进行抑制，对奇数次环流并无作用，因本发明运用注入法在不对称相注入基于冗余率的基频电压。A large number of cascaded sub-modules are potential failure points of the MMC, which poses a great challenge to the operational reliability of the MMC. Once the faulty sub-module is removed, the number of sub-modules of each bridge arm of the MMC is not equal and works in an asymmetrical mode. The invention discloses a fault-tolerant control method of a redundant hot standby MMC, which introduces an odd number of circulating current voltages in an asymmetrical phase, wherein the fundamental frequency component is relatively large, and the fault-tolerant control of the MMC needs to be realized. The asymmetrical circulation leads to problems such as MMC output current distortion, large capacitor voltage ripple, and DC current harmonics and MMC loss increase. Conventional circulating current controllers can only suppress secondary circulating currents, and have no effect on odd-numbered circulating currents, because the present invention uses injection method to inject fundamental frequency voltage based on redundancy rate in asymmetrical phases.
本发明的有益效果是：本发明简单易操作，适用于多个子模块多个桥臂不对称运行工况，有效抑制了MMC中的环流基频分量和谐波，明显减小了MMC的内部损耗，改善了MMC的输出电能质量。The beneficial effects of the present invention are: the present invention is simple and easy to operate, is applicable to the asymmetrical operating conditions of multiple sub-modules and multiple bridge arms, effectively suppresses the fundamental frequency component and harmonics of the circulating current in the MMC, and significantly reduces the internal loss of the MMC , which improves the output power quality of the MMC.
附图说明Description of drawings
图1是本发明实施例中半桥子模块MMC结构图；Fig. 1 is the half-bridge sub-module MMC structural diagram in the embodiment of the present invention;
图2是本发明实施例中的基环流抑制流程图；Fig. 2 is the flow chart of base circulation suppression in the embodiment of the present invention;
图3本发明实施例中的MMC对称运行环流傅里叶分析图；The MMC symmetrical operation circulation Fourier analysis figure in the embodiment of the present invention of Fig. 3;
图4本发明实施例中的MMC不对称运行无容错控制傅里叶分图；Fig. 4 MMC asymmetrical operation non-fault-tolerant control Fourier sub-graph in the embodiment of the present invention;
图5本发明实施例中的MMC不对称运行有容错控制傅里叶分析图。Fig. 5 is a Fourier analysis diagram of the fault-tolerant control of the asymmetric operation of the MMC in the embodiment of the present invention.
具体实施方式detailed description
下面结合附图和具体实施方式，对本发明作进一步说明。The present invention will be further described below in combination with the accompanying drawings and specific embodiments.
实施例1：一种冗余热备用MMC的容错控制方法，所述冗余热备用半桥MMC，如图1所示，每个桥臂中有n个子模块是维持桥臂输出电平数的必需子模块，剩余k个子模块为热备用子模块，n个子模块全部投入时桥臂端口电压与直流侧电压一致。因此，从直流侧电压的角度分析，任意时刻每个桥臂至少有k个子模块处于闲置状态。冗余度r是指MMC热备用冗余保护下冗余模块数与维持系统正常运行必需子模块数的比例关系：Embodiment 1: A kind of fault-tolerant control method of redundant hot standby MMC, described redundant hot standby half-bridge MMC, as shown in Figure 1, there are n submodules in each bridge arm to maintain the output level of the bridge arm Submodules are necessary, and the remaining k submodules are hot standby submodules. When all n submodules are put into operation, the voltage at the bridge arm port is consistent with the DC side voltage. Therefore, from the perspective of the DC side voltage, at least k sub-modules of each bridge arm are in an idle state at any time. Redundancy r refers to the proportional relationship between the number of redundant modules under MMC hot standby redundancy protection and the number of submodules necessary to maintain the normal operation of the system:
当有故障子模块切除时，故障桥臂的冗余度rf为：When the faulty sub-module is removed, the redundancy r f of the faulty bridge arm is:
其中，nf为故障子模块数。为了保证整个桥臂电压的输出电平数不变，子模块故障冗余率rf需不小于0，rf为0时意味着该桥臂没有冗余子模块。Among them, n f is the number of faulty sub-modules. In order to ensure that the output levels of the entire bridge arm voltage remain unchanged, the sub-module failure redundancy rate r f must not be less than 0, and when r f is 0, it means that the bridge arm has no redundant sub-modules.
本实例基于MATLAB/Simulink仿真软件平台搭建了21电平三相逆变MMC仿真模型，仿真参数：系统额定容量S为200MW，交流侧相电压峰值uj(j＝a，b，c)为200kV，直流线路电压为±200kV，桥臂电感值10mH，单个桥臂子模块个数22个，其中两个为冗余子模块。子模块电容为10mF。调制方式为最近电平调制(NLM)，热备用冗余子模块为2个，子模块电容电压平衡控制采用基于完全排序的电容均压策略。This example builds a 21-level three-phase inverter MMC simulation model based on the MATLAB/Simulink simulation software platform. The simulation parameters: the system rated capacity S is 200MW, and the peak value of the AC side phase voltage u j (j=a, b, c) is 200kV , the DC line voltage is ±200kV, the bridge arm inductance value is 10mH, and the number of single bridge arm sub-modules is 22, two of which are redundant sub-modules. The sub-module capacitance is 10mF. The modulation method is Nearest Level Modulation (NLM), and there are two hot standby redundant sub-modules. The sub-module capacitor voltage balance control adopts a capacitor voltage equalization strategy based on complete sorting.
进一步地，具体步骤包括：Further, specific steps include:
Step1：根据冗余热备用MMC数学模型计算出不对称相非对称环流电压表达式；进一步地，以a相为例，相环流电压表达式为：Step1: According to the redundant hot standby MMC mathematical model, calculate the asymmetric phase asymmetric circulating current voltage expression; further, taking phase a as an example, the phase circulating voltage expression is:
其中ucir_asym表示非对称环流分量、rfp，rfn分别表示上下桥臂的冗余比、Id表示环流中的直流分量、ih表示第h次环流谐波分量。Among them, u cir_asym represents the asymmetric circulating current component, r fp and r fn represent the redundancy ratio of the upper and lower bridge arms respectively, I d represents the DC component in the circulating current, and i h represents the hth harmonic component of the circulating current.
Step2：忽略谐波的影响，奇数次频分量的相环流电压表达式为：Step2: Neglecting the influence of harmonics, the phase circulating voltage expression of odd frequency components is:
其中ucir_odd表示奇数次分量，包含基频和三倍频分量。Among them, u cir_odd represents an odd-numbered component, including fundamental frequency and triple frequency components.
Step3：忽略三次环流的影响，得到基频环流的表达式：Step3: Neglecting the influence of the three-time circulation, the expression of the fundamental frequency circulation is obtained:
其中ucir_1表示基频分量。Among them, u cir_1 represents the fundamental frequency component.
Step4：将基频电压注入不对称相参考电压中，采用最近电平逼近调制方法(NLM)进行子模块的投切，其基环流抑制流程图如图2所示。Step4: Inject the base frequency voltage into the asymmetric phase reference voltage, and use the nearest level approach modulation method (NLM) to switch the sub-modules. The flow chart of the base circulation suppression is shown in Figure 2.
本实例仿实例结果如图3所示：MMC对称运行，每个桥臂有22个子模块排序投入，此时a相环流如图3所示，环流里谐波主要是2次分量，谐波畸变率也较低，为1.2％。a相不对称运行在上桥臂切除一个子模块，共有21个子模块排序投入，其它桥臂有22个子模块排序投入，此时a相环流如图4所示，环流里谐波除了2次分量，还有奇数次谐波分量，一基频分量为主，幅值为261.6A，谐波畸变率也较大，为1.55％。如图5所示，本文提出的基频电压注入容错控制明显降低了环流中得基频分量，幅值降为26.9A，同时谐波畸变率也降低为1.33％。The simulation results of this example are shown in Figure 3: MMC operates symmetrically, and each bridge arm has 22 sub-modules sorted into inputs. At this time, the circulating current of phase a is shown in Figure 3. The harmonics in the circulating current are mainly secondary components, and the harmonic distortion The rate is also lower at 1.2%. A-phase asymmetric operation cut off a sub-module in the upper bridge arm, a total of 21 sub-modules are sorted into, and other bridge arms have 22 sub-modules sorted into, at this time, the circulating current of phase a is shown in Figure 4, and the harmonics in the circulating current except for the 2nd order component , There are also odd harmonic components, a fundamental frequency component is dominant, the amplitude is 261.6A, and the harmonic distortion rate is also relatively large, which is 1.55%. As shown in Figure 5, the fault-tolerant control of fundamental frequency voltage injection proposed in this paper significantly reduces the fundamental frequency component in the circulating current, the amplitude is reduced to 26.9A, and the harmonic distortion rate is also reduced to 1.33%.
以上结合附图对本发明的具体实施方式作了详细说明，但是本发明并不限于上述实施方式，在本领域普通技术人员所具备的知识范围内，还可以在不脱离本发明宗旨的前提下作出各种变化。The specific embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Variations.
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